It is known in the construction of internal combustion engines to provide an intake manifold having an induction inlet for a fuel-air mixture which discharges into a mixture plenum that is suitably formed in the head portion thereof and which is located to be heated by the exhaust gases discharged from the engine. In addition, it is known to provide means, as by a chamber surrounding the inlet with suitable openings therefrom into the induction inlet, for supplying recirculated exhaust gases to the induction mixture. Such an arrangement is shown, for example, in U.S. Pat. No. 3,949,715 entitled "Manifold Construction for an Internal Combustion Engine" issued Apr. 13, 1976 to Louis J. Faix, Robert T. Price and James R. Spaulding. Specifically, in this patent, there is disclosed an intake manifold structure formed integral with a cylinder head for use, for example, with an in-line engine and wherein an open bottomed mixture plenum is provided in this structure that is closed by the heated wall of an exhaust manifold whereby to supply mixture heat to the plenum, the plenum receiving an air-fuel mixture through an inlet tube perforated to distribute recirculated exhaust gases from an annular chamber in the structure located between the plenum and the mounting pad thereof used to support a carburetor for the engine.
It is now realized that in intake manifolds, such as of the type disclosed in the above identified U.S. Pat. No. 3,949,715, wherein a heated mixture plenum and a means to effect exhaust gas recirculation are incorporated therein and positioned closely adjacent to the mounting pad for the carburetor, excessive heat can be readily transferred to the carburetor which, as well known, could adversely affect operation of the carburetor.
It is therefore the primary object of this invention to improve an intake manifold for an internal combustion engine whereby the intake manifold structure is provided with an air gap insulator located directly under the mounting pad of the structure whereby to reduce the transfer of heat to the carburetor mounted thereon.
It is another object of this invention to provide an improved intake manifold structure for an internal combustion engine whereby a chamber is provided directly under the carburetor pad of such a structure for admitting air and crankcase ventilation fumes at least to the primary bore extending from the carburetor mounting pad so that the carburetor mounting pad is air cooled.
These and other objects of the invention are obtained in the intake manifold of an internal combustion engine by the provision of an air chamber under the carburetor pad for admitting air and crankcase ventilation fumes to at least the primary bore extending from the carburetor support pad, this air chamber preferably being located above an exhaust gas recirculation supply chamber also surrounding the primary bore and connected thereto to permit exhaust gases to be recirculated into the intake mixture flow through the manifold. The air chamber serves as an air gap insulator to reduce the transfer of heat from the exhaust gases to the carburetor mounted on the carburetor mounting pad of the intake manifold, as well as being operative to improve mixing of the various added gases with the air-fuel mixture entering the intake manifold and to provide for ideal mixture distribution of vacuum supplies.